public class StringBuilderDemo01 {
    public static void main(String[] args) {
        StringBuilder s1=new StringBuilder();
        s1.append("12").append("456");
        System.out.println(s1);
        //反转内容
        s1.reverse();//反转内容
        s1.length();//拿长度
        String res=s1.toString();//转换为字符串

    }
}
